Many people suffer from discomfort caused by damaged articular surfaces between the proximal phalanx and the first metatarsal caused by either rheumatoid arthritis, osteoarthritis or trauma to that portion of the foot. Such discomfort is often aggravated and sometimes precipitated, by frequently wearing pointed-toe ladies' dress shoes or cowboy boots. These pointed-toe shoes apply medial-lateral forces to the big, or great, toe, degrading the lateral head of the first metatarsal.
The prior art has taught prosthetically resurfacing the proximal phalanx using a medical implant having a button-like base and a square or rectangular stem extending downwardly therefrom. Examples of such prior art implants include the Swanson SILASTIC.TM. great toe implant and the Swanson Titanium great toe implant, both manufactured by Dow Corning Wright, 5677 Airline Road, Arlington, Tenn. 38002. The base includes either a flat or simple concave proximal articular surface for articulating with the head of the first metatarsal. A generally planar distal seating surface is provided, opposite the articular surface of the base, for seating against the sectioned portion of the proximal phalanx. A square or rectangular hole is formed in the proximal phalanx during surgery to receive the mating stem of the implant.
The primary deficiency of the prior art proximal phalanx implant is that the proximal articular surface is not shaped to approximate the anatomical convex surface curvature of the head of the first metatarsal, thereby resulting in uneven, tangential contact and increased wear between the implant and the head of the first metatarsal. This increased wear generates particulate debris which contributes to premature failure of the implant. Additionally, use of the square or rectangular stem is less conservative of bone, i.e., requiring significant cancellous portions of the proximal phalanx to be removed, thereby considerably disturbing endosteal blood supply in the proximal phalanx.
The subject invention is directed toward an implant which more naturally articulates with the head of the first metatarsal, provides an extended useful life, causes minimal disturbance to the cancellous portion of the first metatarsal, and is easily implanted during surgery.